Reducing the power consumed by a computer system has two significant advantages: (1) less power must be supplied to the computer system; and (2) less heat must be dissipated by the computer system and by the surrounding environment. On a warm day, many businesses pay both for the electricity to power their computer systems and for the electricity to air condition away the heat their computer systems generate.
Reducing power consumption is especially important in the case of a portable computing system, such as a hand-held or notebook-size computing system. Because the size, weight and storage capacity of a portable battery is limited, conserving power is critical in portable devices, which often must be operable for several hours using only the power supplied by an internal battery. Further, portable devices generally must dissipate the heat they generate without the assistance of the mechanical heat sinks or radiators and cooling fans that can easily be used in a desk-top or rack-mount computer system. Elevated temperatures within a Computing system can make its components operate unreliably or have shortened lifetimes.
Reducing power consumption in desk-top personal computers (PCs) has recently become a major priority. In an office environment, personal computers are often left powered up all day, and sometimes 24 hours a day. In part, this is because booting a PC can take several minutes after power is restored until the PC is usable. In part, PCs are left on because of user inattention to energy conservation. Nevertheless, it is a small percentage of the day, or sometimes even a small percentage of the business day, that a typical PC is actually operating usefully. While a single personal computer consumes only a modest amount of power, they add up--tens of PCs may be left on at a particular business office, and tens of thousands of PCs may be left on in a particular city.
Thus, there is a need for a way to deeply reduce the power consumption of an inactive computer system.
It may be desirable to meet this need by cutting off power to some of the computer system's internal circuits, while leaving it in a state where the lengthy, software-controlled boot process is not required. While such an approach can reduce power substantially, cutting off power to a circuit within a PC has significant disadvantages. First, the isolation field effect transistors (FET's) and multiple power wiring planes that must be added to a computer system to switch off power to portions of its circuitry add significant additional costs to its manufacture. Second, even if the contents of all memories remain undisturbed so as to avoid the boot process, a noticeable amount of time must be allowed for all portions of the circuitry to regain normal operating voltages before any computing activity may resume.
Thus, there is a need for a way to deeply reduce the power consumption of an inactive computer system without significantly increasing its manufacturing costs or requiring significant re-start time.